Reducing the levels of dioxins and dioxin-like PCBs in farmed Atlantic salmon by substitution of fish oil with vegetable oil in the feed

Atlantic salmon were fed extruded diets based on either 100% fish oil (FO) or 100% vegetable oil blend (VO) substitution for 22 months. A total of seven distinct feeding periods were studied that incorporated higher levels of dietary oil inclusion, and larger pellet size as fish size increased. Whole fish levels of polychlorinated dibenzo‐p‐dioxins and dibenzofurans (PCDD/F) and dioxin‐like PCBs (DLPCB) were analysed at the beginning and end of each of the seven feeding periods. The PCDD/F and DLPCB concentrations in the FO diets increased from 2.43 to 4.74 ng WHO‐TEQ kg^?1 (TEQ, toxic equivalents), while VO diets decreased from 1.07 to 0.33 WHO‐TEQ kg^?1 as oil inclusion increased. Partial least square regression analyses identified feed concentration, growth rate and feed utilization, but not variations in lipid content, as factors significantly affecting fish PCDD/F and DLPCB levels. Accumulation efficiencies for DLPCB (740 ± 90 g kg^?1) were significantly (P < 0.01) higher than for PCDD/F (430 ± 60 g kg^?1), explaining the increasing dominance of DLPCB levels over PCDD/F levels in whole fish (DLPCB : PCDD/F ratio of 2.4 ± 0.1 for both VO and FO fed fish) compared with feed (DLPCB : PCDD/F ratio of 1.5 and 0.34 for FO and VO feed respectively). Vegetable oil substitution significantly reduced the level of PCDD/F and DLPCB (eightfold and twelve‐fold, respectively) in the fillet of a 2 kg salmon, but, also negatively affected beneficial health components such as fillet n‐3/n‐6 fatty acid ratio.     

Transfer of toxaphene and chlordane into farmed rainbow trout, Oncorhynchus mykiss (Walbaum) via feed

The study was carried out to quantitate the transfer of toxaphene and chlordane compounds from commercial fish feed into the edible part of rainbow trout, Oncorhynchus mykiss (Walbaum) under normal rearing conditions. Trout were fed with unspiked high energy feed for salmon (fat content 26–30%) over a period of 19 months. The average weight of trout increased from 10 g to more than 2092 g, reaching sizes of 51 cm length. Considerable amounts of toxaphene and chlordane residues were transferred from fish feed into trout muscle. Toxaphene concentrations increased up to 8.6 µg (Σ toxaphene indicator compounds 1–3) kg^?1 wet weight (w.w.) and chlordane reached 5.3 µg Σoxy‐, trans‐, cis‐chlordane + t‐nonachlor kg^?1 w.w. Results are also discussed on the contaminant levels based on the fat content and the effect of sexual maturation is considered in this study. The data allow the establishment of transfer rates for toxaphene and chlordane congeners from high energy diet into the edible part of farmed rainbow trout.     

Influence of dietary fat level and whole-body adiposity on voluntary energy intake by juvenile rainbow trout Oncorhynchus mykiss (Walbaum) under self-feeding conditions

The influence of dietary fat level and whole‐body adiposity on voluntary energy intake of juvenile rainbow trout Oncorhynchus mykiss (Walbaum) was examined using self‐feeders. Groups of lean fish [crude fat (CF) = 7%] and fat fish (CF = 11%), pretreated with a commercial diet with or without supplemental pollock oil, were self‐fed one of three fat level diets (CF = 8%, 13.5% and 19%) for 48 days at 17 °C. Final body weight (BW) and total digestible energy (DE) intake (kJ per fish) were positively affected by the initial BW. Relative to the initial BW, however, fat fish consumed less DE than lean fish. Although the effect of dietary fat level was not significant, percentage weight gain and daily DE intake per BW (kJ kg^?1 BW day^?1) of fat fish were significantly lower than those of lean fish (ancova with initial BW as a covariate, P < 0.05). Energy digestibility, feed efficiency and protein retention were improved with the dietary fat level; however, there was no difference resulting from body fat level. The whole‐body fat levels at the end of the experiment increased with the dietary fat level. Between groups self‐fed the same diet, fat levels of the initially fat fish were still higher than those of the lean fish. The results of the present medium‐term study suggest that rainbow trout adjust DE intake from diets with fat levels ranging from 8% to 19%. Although body fat level affects neither energy digestibility nor protein utilization, a high body fat level may reduce DE intake and consequently depress growth.     

Urea and trimethylamine oxide in diets for seawater farmed rainbow trout: effect on fat belching,skin vesicle,winter ulcer and quality grading

Three experiments were conducted in order to evaluate the effects of urea and trimethylamine oxide (TMAO) supplementation in diets for seawater‐farmed rainbow trout Oncorhynchus mykiss. In all experiments, commercial extruded feed was used as basal control diet, whereas experimental diets were the basal diet supplemented with either 10 g kg^–1 TMAO, 10 g kg^–1 urea or 10 g kg^–1 TMAO and 10 g kg^–1 urea. The experiments were conducted both in research units and in a commercial fish farm. Quality was evaluated in three different commercial slaughterhouses, sorting the rainbow trout into superior, ordinary or processing grade. Significantly more TMAO was observed in muscle of rainbow trout given dietary supplementation of TMAO. However, the levels were low compared with levels in marine fish in general. Trimethylamine (TMA) was not found. No increase in muscle urea content was observed in trout fed urea in the diet. Significantly reduced fat belching, seen as reduced number of fat droplets surfacing in the net pen, was observed in groups given TMAO‐supplemented feeds. At least twice as many rainbow trout with skin vesicles were observed in the control group as in the group fed urea‐supplemented diet. In addition, skin vesicles developed into open sores in the winter only in rainbow trout fed control diet. In a large‐scale trial, quality grading of almost 200 000 market‐sized rainbow trout showed significantly more (88 vs. 83%) trout of superior grade in the group fed dietary urea compared with fish fed control diet. The main reason for downgrading from superior to ordinary and processing grade was skin lesions, supporting the observations made in the experimental units.     

Effects of supplemental dietary l‐carnitine and ractopamine on the performance of juvenile rainbow trout,Oncorhynchus mykiss

This study was carried out to investigate a possible protein‐sparing action of l ‐carnitine and ractopamine in rainbow trout, Oncorhynchus mykiss. An 8‐week feeding trial was carried out to evaluate the effects of supplementation of three levels of l ‐carnitine (0, 1 and 2 g kg^?1) and two levels of ractopamine (0 and 10 mg kg^?1) on growth performance, fillet fatty acid compositions and blood biochemical parameters in a 3 × 2 factorial experimental design. Ractopamine and 1 g kg^?1 carnitine improved the specific growth rate (1.03% and 1.05% day^?1), feed conversion ratio (FCR, 1.3 and 1.29), protein efficiency ratio (PER, 1.88 and 1.85) of fish and crude protein (73.5 and 73.8) content of fish fillet. l ‐carnitine and ractopamine increased the levels of albumin, total protein and globulin in the serum of fish. Apart from eicosapentaenoic acid and docosahexaenoic acid, other fatty acids of fish fillet were increased by ractopamine, while total saturated fatty acids were almost intact. However, the total n‐3 poly unsaturated fatty acids were reduced by l ‐carnitine supplementation (P<0.05). The present study showed that 1 g kg^?1l ‐carnitine and 10 mg kg^?1 ractopamine each can improve the performance of rainbow trout and their combination in diet could enhance the protein level and change the fatty acids profile in fillet muscle.     

Growth performance,nutrient digestibility and lipase activity in juvenile rainbow trout (Oncorhynchus mykiss) fed fat powder in diet containing emulsifiers (cholic acid and Tween‐80)

This research was conducted to investigate the effects of two dietary emulsifiers on nutrient digestibility and lipase activity in rainbow trout (Onchorhyncus mykiss). A basal rainbow trout diet containing fat powder supplemented with 10 and 5 g kg^?1 of cholic acid, and 20 and 40 g kg^?1 of Tween‐80. Control diet contained no emulsifiers with fat powder was replaced by fish oil. Each diet was randomly assigned to 1,500‐L tanks in triplicate. Juvenile rainbow trout with an initial weight of 27.32 ± 2.03 g were randomly distributed in the experimental tanks. The results showed that growth parameters did not change by the addition of the two emulsifiers (p > .05). Total triglyceride content was significantly higher in control fish fed diet containing fish oil (p < .05), while serum cholesterol content showed no significant differences among treatments (p > .05). Control diet resulted in a higher fat digestibility than those of other experimental diets. However, protein and ash digestibilities in diet containing emulsifier were higher than those of the control diet. Control group showed the lowest lipase activity, whereas 20 g kg^?1 Tween‐80 diet caused the highest lipase activity among treatments (p < .05). In conclusion, it seems that a higher lipase activity induced by the emulsifiers could not compensate for the negative impacts of fat powder on the experimental diets.     

Effect of dietary kefir on the growth performance,feed utilization and fatty acid profile of juvenile rainbow trout,Oncorhynchus mykiss

A study was conducted to determine the effect of feeding with diets containing kefir on growth performance and fatty acid profile of rainbow trout (Oncorhynchus mykiss). Four isonitrogenous (450 g protein kg^?1) and isocaloric (4325 kcal kg^?1) diets were prepared in trout feed to contain 0 (control), 20, 50 and 100 g kg^?1 kefir. Fish, initial weight of 46 g, were randomly distributed into triplicate 520‐L fibreglass tanks in freshwater flow‐through system. Fish were fed at 4% of the body weight thrice a day for 12 weeks. The results indicated that survival rate ranged from 97.14 to 100% without significant difference among treatments (p > .05). Whole‐body moisture and lipid composition were significantly affected by diets containing different levels of kefir (p < .05), but no differences were determined in protein and ash. Furthermore, the fatty acid profile of flesh showed differences among the groups. The percentages of saturated fatty acid in the flesh lipid decreased, while 18:3n‐3 and polyunsaturated fatty acids were increased at higher substitution levels of kefir grain. The present study showed that up to 100 g kg^?1 supplementation of kefir in diets could be improve the fatty acid profile, especially PUFA, in fish flesh without adverse effect on the growth, feed utilization and survival rate of rainbow trout.     

Erythromycin and florfenicol treatment of rainbow trout Oncorhynchus mykiss (Walbaum) experimentally infected with Flavobacterium psychrophilum

Flavobacterium psychrophilum is responsible for significant economic losses in rainbow trout aquaculture. Antimicrobial treatment remains the primary means of control; however, there are limited choices available for use. The objectives of the study were therefore to determine the minimum inhibitory concentrations for erythromycin and florfenicol in selected F. psychrophilum isolates and to evaluate their clinical treatment efficacy in experimentally infected rainbow trout. All isolates tested had moderate susceptibility to florfenicol and erythromycin except one isolate, which had low susceptibility to erythromycin. Two isolates (one with moderate and one with low susceptibility to erythromycin) were used in an experimental infection trial. Rainbow trout juveniles were injected intraperitoneally with 10⁸ cfu/fish and after mortality had begun, fish were given erythromycin‐ and florfenicol‐medicated feed at a rate of 75 mg kg^?1 day^?1 and 10 mg kg^?1 day^?1 fish body weight, respectively, for 10 consecutive days. The splenic F. psychrophilum load was determined using an rpoC quantitative PCR throughout the 30‐day trial. Relative to antibiotic‐free controls, erythromycin treatment significantly (p < 0.05) reduced mortality of rainbow trout juveniles infected with FPG101, even when treatment was initiated after clinical signs developed.     

Preliminary study on effects of methionine hydroxy analog and taurine supplementation in a soy protein concentrate‐based diet on the biological performance and amino acid composition of rainbow trout [Oncorhynchus mykiss (Walbaum)]

A feeding trial was conducted on the effects of methionine hydroxy analog (MHA) and taurine supplementation in diets with high levels of soy protein concentrate (SPC) on the growth performance and amino acid composition of rainbow trout, Oncorhynchus mykiss (Walbaum) comparing with fish meal based diet. The control diet had 520 g kg^?1 fish meal. In the methionine deficient diets (5.1 g kg^?1), fish meal was replaced by 490 g kg^?1 of the SPC in the SPC49 diet. The SPC49 diet was supplemented with either MHA (6 g kg^?1) only or a combination of MHA and taurine (2 g kg^?1). Fish were fed isoproteic (460 g kg^?1) and isolipidic (130 g kg^?1) diets for 12 weeks. Growth performance (i.e. weight, feed conversion ratio, and thermal‐unit growth coefficient) was inferior in fish fed the SPC49 diet. MHA supplementation improved growth performance (P < 0.05). No difference was observed when taurine was added to the SPC49 and MHA diet (P > 0.05). Whole‐body taurine contents increased with taurine supplementation, whereas plasma methionine increased with MHA supplementation (P < 0.05). In conclusion, the substitution of fish meal with SPC supplemented with MHA did not negatively impact growth, and the addition of taurine did not improve growth performance in rainbow trout.     

Effect of dietary bovine lactoferrin on growth,haematology and non‐specific immune response in rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the effect of dietary lactoferrin (Lf) on growth, haematology and non‐specific immune response of rainbow trout Oncorhynchus mykiss (Walbaum). Fish were fed an experimental diet containing 0 (as control), 50, 100, 200 and 400 mg Lf kg^?1 diet twice daily for 8 weeks and sampled at 2, 4, 6 (immune function and growth), and 8 weeks (immune function, haematology and growth). Statistical analyses revealed no significant effects of dietary Lf on growth performance (specific growth rate, weight gain, feed conversion ratio, feed intake and condition factor) or haematological parameters (red and white blood cell count, haemoglobin, haematocrit, serum iron and total iron binding capacity [TIBC]). Among the serum non‐specific immune parameters, lysozyme activity increased significantly in fish fed 100, 200, or 400 mg Lf kg^?1 feed for 8 weeks, whereas haemolytic complement activity increased in fish fed 100 and 400 mg Lf kg^?1 diet after 6 weeks. The antiprotease activity increased in groups fed 100, 200 or 400 mg Lf kg^?1 diet after 8 weeks. However, no significant effect was observed on serum peroxidase level. It can be concluded that feeding of rainbow trout on the diet supplemented with 100 mg kg^?1 or higher for 8 weeks enhances the non‐specific immune response.     

Dietary yeast culture supplementation improves initial rearing of McConaughy strain rainbow trout

The addition of a yeast culture food supplement (DVAqua from Diamond V. Mills, Cedar Rapids, IA, USA) was evaluated during feeding of McConaughy strain rainbow trout Oncorhynchus mykiss. Two trials were run consecutively, starting with initial feeding, and were replicated over 2 years. The yeast culture was added to commercial trout starter at levels of 0.125 and 0.25 g kg^?1. The number of rainbow trout that died during the first 4 weeks of rearing was significantly reduced in the tanks receiving either of the yeast culture‐supplemented diets compared with the tanks receiving a control starter diet. Ending tank weights and gain were significantly and consistently greater in the tanks fed the 0.25 g kg^?1 yeast culture diet. Individual fish weights were also significantly heavier in the fish‐fed yeast culture containing diets in each year of the study at the end of 27 days. In the trials from 4 to 8 weeks postinitial feeding, mortality rates were significantly less only in the tanks receiving 0.25 g kg^?1 yeast culture supplementation. Individual fish lengths and weights at the end of the second trial were significantly greater in the tanks receiving either level of yeast culture compared with the control diet only in 1 year. Total tank weights and feed conversion were not significantly different between any of the treatments. The inclusion of DVAqua yeast culture provided significant increases in trout survival and growth through the first 4 weeks of feeding, with continued benefits for the next 4 weeks.     

Effects of diludine supplementation on growth performance,liver antioxidant enzyme activities and muscular trace elements of rainbow trout (Oncorhynchus mykiss) juveniles at a low water temperature

Diludine is used as an effective agent reducing mutagenic effects of environmental pollutants, increasing productivity and protecting reproductive system of parental individuals and quality of their offspring. A 10‐week study was conducted to evaluate potential effects of diludine on rainbow trout (Oncorhynchus mykiss) juveniles growth performance, feed utilization, survival rate, liver antioxidant enzyme activities (superoxide dismutase, SOD, EC1.15.1.1 ; catalase, CAT, EC1.11.1.16 ; glutathione peroxidase, GPx, EC 1.11.1.9 ; glutathione reductase, GR, EC1.6.4.2 ; glucose‐6‐phosphate dehydrogenase, G6PD, EC1.1.1.49 and glutathione S‐transferase, GST, EC1.5.1.18 ), the levels of malondialdehyde (MDA) as a lipid peroxidation marker and muscular trace elements at a low water temperature (9 °C). Diludine was added at 0.2, 0.5 and 1 g kg^?1 to a fish meal–based control diet, and each diet was fed to triplicate groups of rainbow trout juveniles. After 10 weeks, there were no differences in survival rate between fish fed experimental diets (P > 0.05). It was observed that a significant improvability existed for both growth and feed utilization in fish fed diets supplemented with diludine (P < 0.05). Antioxidant enzymes showed significantly increased activity in liver tissues (P < 0.05) and then a decrease to initial activity levels during the experimental time. (GPx activity was not determined in the juvenile livers.) SOD and GST activities in liver of fish fed the diets with diludine tended to be higher and GR activity tended to be lower than that in fish fed the basal diet. However, in general, it was determined that different concentration of diludine did not affect the studied antioxidant enzyme activities except G6PD in the liver of juveniles fed the diet with 1 g kg^?1 diludine. On the other hand, the significant reduction was found in MDA levels in the fish fed the diets with diludine compared with basal diet on the 14th and 28th days of experiment. It was also observed that Cu, Fe, Mg, Zn and Se levels were significantly higher in the juveniles fed the diet with 1 g kg^?1 diludine than those fed the basal diet. In conclusion, the results of this trial indicate that 1 g kg^?1 dietary supplementation with diludine seems to be most positive for rainbow trout production in cold‐water adaptation.     

Aqueous fractionation improves the nutritional value of wheat distillers grains for rainbow trout (Oncorhynchus mykiss)

Fractionation of wheat wet distillers grains (WWDG) was performed to reduce non‐starch polysaccharides (NSP) and increase protein content. WWDG was collected from two ethanol plants, and protein was extracted by the addition of water, autoclaving to precipitate protein and drying in a forced air oven at 55 °C to create WWDG–protein concentrate (WWDG–PC). This process increased crude protein (CP) and decreased NSP in the WWDG–PC (P < 0.05). Dry matter and energy digestibility of WWDG–PC in rainbow trout were increased by fractionation (P < 0.05). A 56‐day growth trial was performed to determine the effect of feeding WWDG–PC on growth performance of rainbow trout. Rainbow trout (n = 18/tank; body weight = 231 g; 3 tanks/treatment) were fed diets containing 0, 75, 150, 225 or 300 g kg^?1 WWDG–PC. All diets were formulated to contain 386 g kg^?1 digestible CP and 17.6 MJ kg^?1 digestible energy. There was no significant linear or quadratic relationship between inclusion rate and growth, feed intake or feed conversion, indicating that at inclusion levels of up to 300 g kg^?1 of WDDG–PC does not reduce the growth performance of rainbow trout.     

An evaluation of DVAqua®, a fully‐fermented yeast culture,during long‐term hatchery rearing of McConaughy strain rainbow trout

The addition of a proprietary, fully‐fermented yeast Saccahromyces cerevisiae culture supplement (DVAqua^®, Diamond V Mills, Cedar Rapids, IA, USA) was evaluated during long‐term feeding of McConaughy strain rainbow trout Oncorhynchus mykiss. Beginning at initial feeding and continuing for 408 days of hatchery rearing, the trout received either a commercially‐manufactured feed or the same feed containing 0.125 g kg^?1 DVAqua. This study was conducted at a production level as part of normal (real‐world) hatchery operations, with the fish periodically inventoried and moved into different rearing units. Although no rearing‐tank replication occurred during the first 54 days of feeding, multiple tanks and raceways were used thereafter. Fish in rearing units receiving DVAqua supplementation exhibited less mortality, particularly during the earlier rearing stages. During the final 177 days of rearing in six raceways, DVAqua‐fed McConaughy strain trout were significantly larger and had a significantly improved feed conversion ratio. The overall feed conversion ratio for the entire duration of the study was 1.17 in the fish receiving DVAqua supplementation compared to 1.21 in the control group. Despite the limitations of this study, the use of DVAqua is recommended for McConaughy strain rainbow trout and other less‐domesticated, more difficult‐to‐rear salmonids.     

Optimizing zinc supplementation levels of rainbow trout (Oncorhynchus mykiss) fed practical type fishmeal‐ and plant‐based diets

Rainbow trout (23.1 ± 0.4 g) were fed either a fishmeal‐ or plant‐based diet supplemented with various levels of zinc (0, 15, 30, 60 or 120 mg kg^?1) for 12 weeks. Trout fed the fishmeal diet had significantly higher weight gain than with the plant‐based diet. Zinc supplementation in the fishmeal diet had no effect on growth performance, suggesting that additional dietary supplementation of zinc is not required. However, in trout fed the plant‐based diet, growth increased significantly up to 30 mg kg^?1 zinc after which growth was not affected. Trout fed the plant‐based diet containing no zinc exhibited severe growth retardation, and in fish fed the 0 and 15 mg kg^?1 zinc diets, cataracts were present. Use of broken‐line quadratic modelling suggests that dietary supplementation of zinc needed to prevent deficiency and promote adequate growth in rainbow trout fed the plant‐based diet in this study was 30.1 mg kg^?1 (80 mg kg^?1 total dietary zinc). This is higher than the NRC (2011, Nutrient Requirements of Fish and Shrimp) dietary recommended level of 15 mg kg^?1 for rainbow trout. Following the NRC recommendation could lead to zinc deficiency in rainbow trout fed a plant‐based diet.     

Dietary uptake of dioxins (PCDD/PCDFs) and dioxin-like PCBs in Atlantic salmon (Salmo salar)

Atlantic salmon (Salmo salar) were fed graded levels of dioxins (polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans) and dioxin‐like polychlorinated biphenyls (DLPCBs) in their diets for 7 months. The dioxin and DLPCB concentrations in both fillet and whole body of salmon increased with increasing dietary exposure. DLPCBs transferred more efficiently from the feed to edible flesh of salmon than dioxins, and contributed a higher proportion to the total toxic equivalents (TEQ). At the end of the trial, the maximum concentrations of dioxins in fillet and whole fish were 1.9 and 2.3 pg WHO‐TEQ g^?1 fresh weight, respectively. Hence with this feeding period even with the most contaminated feed (4.9 pg WHO‐TEQ g^?1 dw) the dioxin concentrations in salmon did not exceed the maximum level set by the European Commission [4 pg WHO‐TEQ g^?1 (EC 2375/2001)]. The inclusion of DLPCBs in this study provides valuable information for forthcoming risk assessments and the future establishment of maximum limits for these compounds in feed and fish.     

Effects of supplementing methionine hydroxy analogue in soybean meal and distiller's dried grain-based diets on the performance and nutrient retention of rainbow trout [Oncorhynchus mykiss (Walbaum)]

Two experiments were conducted to evaluate the effects of supplementing methionine hydroxy analogue (MHA) on the performance, body composition, and nutrition retention of rainbow trout. In experiment 1, a 2×4 factorial arrangement with two MHA supplemental levels (with and without) and four fish meal replacement levels (25%, 50%, 75%, and 100%, replaced with soybean meal (SBM) and wheat gluten) was used. A fish meal diet was included as a control. Results showed that fish meal replacement levels had significant effects on fish weight gain (WG), feed conversion ratio (FCR), body moisture, crude protein, crude fat, and ash (P<0.05). In experiment 2, a fish meal reference diet and seven other diets were made using SBM and distiller's dried grain with solubles supplemented with 0, 0, 0.55, 1.1, 1.65, 2.2, and 2.75 g MHA kg^?1 diet to replace 50% of fish meal. WG, FCR, and apparent retention of crude protein and phosphorus were significantly improved in rainbow trout fed the diet containing 1.65 g MHA kg^?1 diet compared with fish fed an equivalent diet without MHA.     

Rainbow trout silage as immune stimulant and feed ingredient in diets for Mozambique tilapia (Oreochromis mossambicus)

Peptides and free amino acids resulting from protein hydrolysis could act as stimulants of fish non‐specific immunity. The study aimed to determine the potential of rainbow trout viscera silage as immune stimulant and feed ingredient for Mozambique tilapia, and to establish whether formic acid used during silage preparation contributed to any effects. Four diets were evaluated: a reference diet (R), one containing 6.5 g kg^?1 formic acid (FA) and two silage diets containing 160 g kg^?1 (SL, low inclusion) and 285 g kg^?1 (SH, high inclusion) silage. Low silage inclusion improved phagocytic activity of leucocytes compared with the reference, while high inclusion showed no improvement. No other non‐specific immunity parameters or haematology were affected by any treatments. High silage inclusion significantly decreased growth and led to higher mortality, while formic acid had no effect on growth. It is concluded that rainbow trout viscera silage can stimulate the cellular non‐specific immunity of Oreochromis mossambicus, and that protein hydrolysis products (and not formic acid) is responsible for the stimulation. The silage can also serve as source of dietary protein and essential amino acids in tilapia diets. However, both fish growth performance and improvement in cellular immunity are dependent on silage inclusion level.     

A comparison of the growth performance of rainbow trout (Oncorhynchus mykiss) when fed soybean,narrow‐leaf or yellow lupin meals in extruded diets

This study compared the effect of increasing dietary inclusion of soybean, narrow‐leaf lupin or yellow lupin kernel meals when fed to rainbow trout. Each meal was formulated into a test diet to create a series of inclusion levels of 0, 100, 200, 300 and 400 g kg^?1. Each diet was formulated to the same digestible protein and energy specifications. The diets were fed to apparent satiety to 30.0 ± 0.71 g rainbow trout for 28 days. After this period, fish in the reference (0 g kg^?1) treatment attained a weight of 93.2 g. Growth of the fish among the treatments was observed to be improved by the addition of either variety of lupin meal. In contrast, growth of fish fed the soybean meal was equivalent to that of the 0 g kg^?1 fish meal reference, but was poorer at the 400 g kg^?1 inclusion level. Feed intake with the lupin meals was marginally improved with lupin inclusion, but at the higher soybean meal inclusions, feed intake was reduced relative to the fish meal reference diet. The inclusion of the different grains also had significant effects on the physical properties of the pellets.